1. Field of the Invention
The present invention relates generally to a method and system for merging multiple push-to-talk over cellular (PoC) sessions which, when group members belonging to one PoC group session want to participate in another PoC session under the environment of multiple PoC group sessions, establishes a new session by merging PoC group sessions without releasing the currently participating PoC session.
2. Description of the Related Art
With recent developments in mobile communication technology as well as expansion of communication networks, service and applications using a mobile phone are now more diversified and expansive. Further, user demand has been extended from simple communication service toward location service, multimedia service, PTT (Push-to-Talk) service, and so forth. In particular, the PTT service supports various additional functions, such as an instant messenger, a status indication, etc, inclusive of group communication and voice communication which was possible only with a radio set, a TRS (Trunked Radio System), etc., in the past.
Currently, there is a lively discussion to enact a standard of PTT over Cellular (PoC) service that serves a concept of the PTT using a mobile communication network. The PoC service has various features distinguished from the existing mobile communication service. One of the features allows a user to, because he/she belongs to a plurality of sessions, make a call while moving between the sessions if necessary. The requirement that the user should be allowed to make the call while moving between the plurality of sessions is specified in requirements of an OMA (Open Mobile Alliance), which is a group that defines mobile communication services.
Hereinafter, a structure of a general PoC service system will be described.
FIG. 1 is a conceptual view showing a general PoC basic structure. Referring to FIG. 1, a PoC client 10 is a service requester that is mounted in a mobile phone, and usually connected to a network based on a SIP/IP (Session Initiation Protocol/Internet Protocol) core 30 through an access network 20, wherein the SIP/IP core-based network is a core network for supporting SIP and IP multimedia.
Here, the PoC client 10 makes it possible to provide access to PoC service while residing in a PoC user terminal. The PoC client 10 has main functions such as originating a PoC session, participating in an existing PoC session, and terminating the established PoC session, in the aspect of a PoC user. In addition, the PoC client 10 performs other functions such as creating and sending a talk burst, supporting an instant personal alert, and providing authentication when getting access to the PoC service. Hereinafter, as long as a separate reference is not required, the term “PoC client 10” is used in the same meaning as a PoC service subscriber.
The SIP/IP core-based network is connected to a PoC server 60, a GLMS (Group List Management System) 50 and a presence server 70 in order to support the PoC service, thereby providing the PoC service. The PoC server 60 performs a Controlling PoC Function (hereinafter, referred to as “CF”) for maintaining and managing the PoC session, a Participating PoC Function (hereinafter, referred to as “PF”) for participating in the PoC session opened for one-to-one communication or many-to-many communication, and so forth.
Hereinafter, the CF and the PF functions will be described in more detail with reference to the following Tables 1 and 2, respectively.
TABLE 1Controlling PoC Function (CF)Provides centralized PoC session handlingProvides the centralized Media distributionProvides the centralized Talk Burst Arbitration functionality includingtalker identificationProvides SIP session handling, such as SIP session origination,termination, etc.Provides policy enforcement for participation in group sessionsProvides the participants informationCollects and provides centralized media quality informationProvides centralized charging reportsMay provide transcoding between different codecsSupport Talk Burst Control Protocol Negotiation
As shown in Table 1, the CF function performs, among functions of the PoC server, a function that serves to manage the PoC sessions on the whole, particularly to receive, sequence and authorize the right-to-speak (or floor) request of the PoC clients, to distribute a talk burst requested by an arbitrary PoC client to all the other PoC clients participating in group calling, and to provide information of the PoC clients participating in the group calling.
As shown in Table 2, the PF function serves to manage the sessions that are connected with the CF and the respective PoC clients in the PoC session. In particular, the PF function serves to relay the right-to-speak when the PoC client requests the right-to-speak or when the right-to-speak is assigned to the PoC client in the CF function. Further, the PF function serves to relay media between the CF function and the PoC client, to perform transcoding when different codecs are used between the CF function and the PoC client, and to filter any one of two simultaneous sessions according to selection of a PoC user when the PoC user is invited to one session while participating in the other session.
TABLE 2Participating PoC Function (PF)Provides PoC session handlingMay provide the Media relay function between PoC client and ControllingPoC serverMay provide user media adaptation proceduresMay provide the Talk Burst control message relay function between PoCclient and Controlling PoC serverProvides SIP session handling, such as SIP session origination, terminationetc., on behalf of the represented PoC client.Provides policy enforcement for incoming PoC session (e.g. accesscontrol, incoming PoC session barring, availability status, etc)May collect and provide media quality informationProvides the participant charging reportsMay provide filtering of the media streams in the case of simultaneoussessionsMay provide transcoding between different codecsMay support Talk Burst Control Protocol NegotiationStores the current Answer Mode and Incoming PoC Session Barringpreferences of the PoC client
Meanwhile, in order to open the many-to-many session, the PoC service system requires management of PoC participation groups intended for participation and management of a list of the PoC participation groups, and includes a server for the GLMS 50 which provides the PoC participation groups and their list, and a GLMS manager or administrator 40 that performs management of the GLMS server.
Further, the PoC service system includes the presence server 70 that provides and manages information on an individual or group to whom the PoC service is provided. Finally, the PoC service system should include a remote PoC network 80 that represents the SIP/IP core-based network, the PoC server, etc. for connection with another user when communication between individuals or between the individual and the group is performed in the PoC service.
In the PoC system configured as mentioned above, a certain PoC user can input information on the group and its members into the GLMS 50 by means of his/her own terminal, and can know information of other PoC users who can be called out through an individual or group list received from the GLMS 50. Another method capable of generating, correcting and managing the group and its members in the GLMS 50 can input such information through a communication network, such as an Internet, an intranet.
In order to make use of PoC calling service, the PoC user registers his/her PoC address with the SIP/IP. At this time, the SIP/IP core 30 stores information on the PoC user on the basis of a request of the PoC user. Therefore, when attempting PoC group calling, another PoC user registers his/her own information with the SIP/IP core-based network in advance as set forth above, and sends a calling request to his/her own SIP/IP core-based network using group identification information received from the GLMS 50. At this time, the SIP/IP core 30 performs address resolution and domain location resolution using the information of the requesting PoC user, and then sends a PoC communication request to a home PoC server with which the requesting PoC user is registered. The PoC server prepares the establishment of the PoC session in response to the PoC communication request, obtains information of each PoC user from a GLMS server, and sends a communication request signal to the corresponding SIP/IP core-based network. At this time, in the case of the communication requests of the users within an intra-domain, the PoC server performs the functions of both the PF and the CF. The PoC server managing the PoC user who receives the communication request locates the SIP/IP core-based network using the information of the PoC user which is sent to the PoC server, and then sends the communication request to the PoC user.
Hereinafter, a general PoC communication procedure having the above-mentioned features will be described with reference to FIG. 2, which is a flowchart showing a procedure of establishing a general PoC session.
Referring to FIG. 2, a PoC client A sends information on an individual or group, with whom the PoC client A wants to talk, to a SIP/IP core A through an INVITE message. The SIP/IP core A checks a parameter designating PoC service from the information of the INVITE message, and sends an INVITE request to a PoC server A which takes charge of the PoC client A. The PoC server A has a difference in realizing functions of a home PoC server according to a type of a PoC call. In other words, when directly establishing the PoC session, like a one-to-one or ad-hoc group call, the PoC server A is so realized that its own home PoC server performs the PF and CF functions at the same time, and sends the INVITE message to a PoC server B which takes charge of a PoC client B. In the case of a pre-arranged group call, in which clients participate in a previously originated session, a management function of the session cannot be realized in the home PoC server, and thus the INVITE message is sent to the PoC server A that performs the CF function on the session. At this time, the SIP/IP core serves as a passage through which the INVITE message is transmitted as mentioned above, and actually serves to perform address resolution of the PoC server B or PoC server A. When the INVITE message transmitted in this manner is transmitted to a PoC client B, the PoC client B sends an alerting response (e.g., ringing, light, beep etc.) to the PoC client A. When a PoC user B receives a PoC call, an OK response is transmitted to the PoC client A, so that the PoC call is connected. Next, the PoC client A receives a floor (right-to-speak) from a server performing the CF function, and thereby PoC communication is ultimately performed.
The prior art for the PoC service assists the PoC user in participating in one or more PoC sessions. When one group session desires a group communication with group members of another PoC session, group members of the PoC session which wants to be merged with another PoC session each send a session termination message to the session to which each member belongs, and then participate in the group communication by request of new session participation in a session in which each member wants to participate. Further, this procedure is applied to all of the members, each of whom wants to participate in the session. At this time, the session which originally wants to be merged is terminated.
Hereinafter, a conventional PoC communication procedure for connecting with another PoC session will be described with reference to the FIG. 3, which is a flowchart showing a method of merging with another PoC session.
Referring to FIG. 3, a PoC session Y is one group session that wants to be merged, and a PoC session X is a group session that requests session merging. In the prior art, in order to be merged with a previously activated session, the PoC session X first sends a termination signal (PoC Session Bye) to a PoC server X that manages a currently ongoing session. In this process, the PoC session X causes a media parameter, which is reciprocally negotiated between a server and a client, to be released. Subsequently, after termination of an existing session, a PoC client makes a new INVITE request. Here, the PoC client X requires an identity of a group session that wants new participation (to be merged) so as to determine a server intended to send the INVITE request. To this end, the PoC client X makes use of address information such as a conference URI (Uniform Resource Identifier).
Finally, after receiving a session participation request from the PoC client X, a PoC server Y sends an OK message to the PoC client X, which requested the PoC session, by means of policy within the PoC server or approval of group members in response to the session participation request. Thereby, the merged session managed by the PoC server Y is configured, and a Talk Burst Control procedure for arbitrating the right to speak in the PoC communication is performed.
Hereinafter, the session which wants to merge (in FIG. 3, the PoC session X) is called a merging session, while the session to be merged (in FIG. 3, the PoC session Y) is called a merged session. Further, among the functions of the PoC server, the controlling PoC function is abbreviated as CF, and the participating PoC function is abbreviated as PF.
In the prior art as mentioned above, when the group members belonging to an arbitrary PoC group session want to participate in another PoC session under the environment of the multiple PoC group sessions, it is not until the currently participating PoC session is released that the group members establish the session with another group.